The present invention relates to a recording paper, and in particular, relates to a recording sheet for an ink jet printer, in which printing density is high and vivid; ink absorptivity is superior; light resistance, shelf-life in a room, yellow stain prevention and water resistance are excellent; fading and changing of color tone in direct sunlight can be avoided; and ink is quickly absorbed, thereby satisfying high speed printing technique requirements in the future.
The use ink jet printers is further increasing in recent years since they have characteristics such as vividness of recording images, quiet operation, ease of coloring, and the like. In order to prevent the jet nozzle from being blocked due to drying of ink, an ink which is difficult to dry must be used in the ink jet printer. As ink having this property, water-soluble ink which is dissolved or dispersed with adhesive, dye, solvent, additives, or the like, in water, is generally employed. However, a letter or an image formed on the recording sheet by employing the water-soluble ink is inferior to that of printed matter or silver halide photographs due to the use of pigment-type inks, from the viewpoint of light resistance, shelf-life in a room, water resistance, and resistance to direct sunlight.
In recent years, as ink jet printers become less expensive and high vividness and colorfulness of the printing image is anticipated, the requirements for various properties such as light resistance are gradually becoming severe. Therefore, completely satisfying these various requirements such as light resistance is an essential goal for recording sheets for ink jet printers.
In consideration of this present situation, improvement of the light resistance of recording sheets for ink jet printers is being studied. Many patent applications, for example, typified by Japanese Patent Publication No. 4(92)-15745, proposes adding metallic compounds such as magnesium oxide, magnesium carbonate, calcium oxide, calcium carbonate, or the like to improve light resistance. However, it has been confirmed that an improvement in light resistance by merely adding these metallic compounds is not sufficient and a drawback is that a decrease in vividness of images results. Additionally, with regard to conventional methods of improving yellow stain prevention of recording sheets for ink jet printers, many patents, for example, typified by Japanese Patent Unexamined Publication (Kokai) No. 8(96)-169177, are applied for. However, these improvements are not yet sufficient and are not put to practical use. Furthermore, with regard to light resistance, resistance to the room light has been studied; however, preventive methods for fading and changing of color tone in direct sunlight have not been researched sufficiently.
Therefore, an object of the present invention is to provide a superior recording sheet for an ink jet printer which sufficiently satisfies various property requirements such as light resistance of images.
According to the results that the inventors have derived from various studies with regard to a recording sheet for an ink jet printer, the various properties, such as the light resistance of images, are improved very effectively by including a specific salt in an ink receiving layer, and have thereby attained the present invention. In other words, the present invention provides a recording sheet for an ink jet printer including a water-soluble divalent or greater metallic salt. In the following, the preferred embodiments according to the present invention will be explained in detail.
The recording sheet for an ink jet printer according to the present invention is a lamination in which is provided at least one ink receiving layer on at least one surface of a base material by a providing means such as a coating method, or the like. The ink receiving layer may be provided as two layers or more. In the following, materials which consist of a base material and an ink receiving layer will be explained.
As a base material provided for coating an ink receiving layer and a back coat layer according to the present invention, a base paper which is mixed wood pulp such as chemical pulp such as LBKP, NBKP, or the like; mechanical pulp such as GP, POW, RMP, TMP, CTMP, CMP, CGP, or the like; recycled pulp such as DIP, or the like; etc.; or synthetic fiber pulp such as polyethylene fiber, or the like, as a primary component, with pigment and any type of additive which is usually employed in paper such as sizing agent, yield improving agent, strength agent, or the like, alone or in combination, as necessary, and produced by using any type of apparatus such as a fourdrinier paper machine, cylinder paper machine, twin wire paper machine, or the like; can be preferably employed. In addition, a base paper provided with starch, polyvinyl alcohol, or the like using a size press; a base paper provided with an anchor coat layer; a coated paper such as art paper, coated paper, cast coat paper, or the like, on which is provided with a coat layer on these base papers, can be preferably employed. These base papers and coated papers may provide an ink receiving layer directly, and in order to control flattening of the paper, a calender apparatus may be used such as a machine calender, TG calender, soft calender, or the like, before coating the ink receiving layer.
As a base material, a polyolefin resin layer may be provided on the surface of the above-described base paper, and synthetic resin such as polyethylene, polypropylene, polyester, nylon, rayon, polyurethane, or the like; film material comprised of mixture with these; and fiber-formed sheets of these synthetic resins may be employed.
(A) Pigment
In an ink receiving layer according to the present invention, generally used pigments which are insoluble or slightly soluble in water can be employed alone or in combination. For example, a white inorganic pigment such as precipitated calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomite, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, colloidal alumina, pseudo-boehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrolytic halloysite, magnesium carbonate, magnesium hydroxide, or the like; an organic pigment such as styrene-type plastic pigment, acrylic-type plastic pigment, polyethylene, microcapsules, urea resin, melamine resin, or the like, etc., can be employed.
Of these pigments, as white pigment which is a primary component contained in an ink receiving layer, porous inorganic pigment is preferable since drying properties and absorptivity of an ink for an ink jet printer is excellent. For example, porous synthetic amorphous silica, porous magnesium carbonate, porous alumina, or the like, are preferably employed. Of these, since both printing quality and shelf-life (shelf-life in a room or in direct sunlight) are satisfied in the present invention, the precipitation type or the gel type of porous synthetic amorphous silica with a specific surface of about 200 to 600 g/m2 can be preferably employed.
(B) Binder Resin
As binder resin contained in an ink receiving layer according to the present invention, polyvinyl alcohol, silyl modified polyvinyl alcohol, vinyl acetate, oxidized starch, etherificated starch, casein, gelatin, soybean protein; cellulosic derivative such as carboxymethyl cellulose, hydroxyethyl cellulose, or the like; conjugate diene type copolymer latex such as maleic anhydride resin, styrene-butadiene type copolymer, methylmethacrylate-butadiene copolymer, or the like; acrylic type polymer latex such as (metha)acrylic acid ester polymer, (metha)acrylic acid ester copolymer, or the like; vinylic type polymer latex such as ethylene-vinylacetate copolymer, or the like; functional group modified polymer latex comprised of monomer including functional groups such as carboxy group, or the like of all types of these polymers; water-soluble adhesive consisting of thermosetting synthetic resin such as melamine resin, urea resin, or the like; synthetic resin type adhesive such as polymethylmethacrylate, polyurethan resin, unsaturated polyester resin, vinylchloride-vinylacetate copolymer, polyvinylbutyral, alkyd resin, or the like, can be preferably employed. These can be employed alone or in combination.
The compounding ratio of the pigment to the binder resin in the ink receiving layer is preferably 1/1 to 1/15, and is more preferably 1/2 to 1/10.
(C) Water-Soluble Divalent or Greater Metallic Salt
A general ink receiving layer of a recording sheet for an ink jet printer is comprised of the above-described pigment and binder resin as primary components; however, the main feature of the present invention is that a water-soluble divalent or greater metallic salt is additionally included in an ink receiving layer. In this case, xe2x80x9cwater-solublexe2x80x9d means that 25 g or more of inorganic metallic salt by anhydrous weight is dissolved in 100 g of saturated solution, when saturated solution with metallic salt employing water at 20xc2x0 C. as solvent is prepared. The xe2x80x9cdivalent or greater metallic saltxe2x80x9d means that a divalent or greater metallic cation formed when the salt is dissolved and electrolyzed in water or the like. As a metallic salt, a water-soluble divalent or greater metallic salt can be employed in an appropriate ratio. Particularly, halogenide or hexafluorosilicate of typical elements such as magnesium, calcium, strontium, barium, gallium, indium, thallium, germanium, tin, lead, bismuth, or the like; inorganic metallic salts such as sulfate, thiosulfate, phosphate, chlorate, nitrate, or the like have good solubility and excellent improvement. Water-soluble salts of organic acid can be also employed. Since these salts scarcely cause light scattering which caused by insoluble salt, etc., in the ink receiving layer or the like, there is no problem in that the color image is somber in printing, whereby these are preferably employed.
For example, magnesium chloride, calcium chloride, barium chloride, tin chloride, lead chloride, magnesium sulfate, calcium sulfate, magnesium chlorate, magnesium phosphate, magnesium nitrate, barium nitrate, calcium nitrate, or the like, can be preferably employed. The metallic salt content to total solid of the ink receiving layer is preferably in any ratio, is more preferably ranging from 1.0 to 40.0% by weight, and is most preferably ranging from 5.0 to 20.0% by weight. In the case in which the content is less than 1.0% by weight, sufficient effects of light resistance of images and various properties are not confirmed. In the case in which an amount of more than 40.0% by weight is added, although light resistance and the various properties are sufficiently improved, further improvement is not expected. Moreover, water resistance, moisture resistance or strength of ink receiving layer may decrease and control of printing quality of ink jet images may be difficult. In order to obtain vividly printed images, suitable ranges of these contents to the pigment in the ink receiving layer are preferably 5.0 to 40.0% by weight, and are more preferably 10.0 to 20.0% by weight. In order to maintain superior vividness, the coating weight of the metallic salt is preferably 0.2 to 10.0 g/m2 by weight.
In addition, these metallic salts may be employed by coating on the base material so that the coating weight of the salt is about 0.2 to 20.0 g/m2, or by adding in the base material so that the concentration of the salt is about 0.5 to 20.0% by weight.
(D) Other Additives
Furthermore, as other additives added to the ink receiving layer, cationic dye fixing agent, pigment dispersing agent, thickener, fluidity improving agent, defoaming agent, foam inhibitor, surface lubricant, foaming agent, penetrating agent, color dye, color pigment, fluorescent brightening agent, UV absorber, antioxidant, antiseptics, water resistant agent, hardening agent, or the like, can be blended in an appropriate ratio, as necessary.
Of these additives, in particular, the cationic dye fixing agent may cooperate with the water-soluble divalent or greater metallic salt in improvement of the light resistance. In order to obtain light resistance and water resistance and to improve these effectiveness, the solid content ratio of the water-soluble divalent or greater metallic salt with respect to the cationic dye fixing agent in the ink receiving layer is preferably 1/4 to 4/1, and is more preferably 1/1 to 3/2.
The composition of the ink receiving layer according to the present invention is not limited to the above-described materials. In order to satisfy various properties such as light resistance and to solve the productive problems such as adhesion to the base material, powdering of the layer (pigments fall off in the layer) in the cutting process, or the like, the solid content ratio of each material in the ink receiving layer is most preferably 40.0 to 60.0% of pigment (preferably silica and/or alumina) by weight, 20.0 to 40.0% of binder resin by weight, and 1.0 to 40.0% of water-soluble divalent or greater metallic salt by weight.
The ink receiving layer is formed on a supporting material by coating the coating material which was prepared by dissolving or dispersing in a suitable solvent, such as water or alcohol, completely dissolving divalent metallic salt, or the like, using various kinds of apparatus such as a blade coater, roll coater, air knife coater, bar coater, rod blade coater, size press, or the like on-machine or off-machine as appropriate. The coating weight of the ink receiving layer in the one layer type is preferably 5.0 to 30.0 g/m2, and is more preferably 5.0 to 20.0 g/m2. In the case of the two layer type in which is provided the first ink receiving layer on a base material and in which is provided the second ink receiving layer on the first ink receiving layer, the coating weight of the first ink receiving layer is preferably 5.0 to 30.0 g/m2, and is more preferably 5.0 to 20.0 g/m2.
In addition, the coating weight of the second ink receiving layer is preferably 5.0 to 15.0 g/m2, and is more preferably 5.0 to 10.0 g/m2. In the case in which the coating weight is less than in the above range, excellent ink absorptivity or fixativity is seldom obtained. In the case in which it is more than in the above range, the problems such as powdering of the layer, decrease of the productivity, increase in cost or the like is caused. In particular, in the case in which the coating weight of the second ink receiving layer is more than 15 g/m2, it is difficult for the ink to pass through to the second ink receiving layer, thereby causing blurring of ink, so that vividness of images is impaired. In this way, it is preferred that the coating weight of the ink receiving layer be controlled according to the number of the provided ink receiving layers. In the case in which two or more ink receiving layers are provided, the metallic salts may be contained in any of the ink receiving layers, or may be contained in some of the ink receiving layers. In the case in which the metallic salts are contained in some ink receiving layers, in order to reduce the concentration difference between the layers, the content of the metallic salts contained in the layers is preferably the same ratio.
The coated ink receiving layer may be finished, using a calender such as a machine calender, TG calender, super calender, soft calender, or the like.
The recording sheet for an ink jet printer according to the present invention is constructed as described above, and even the construction which provided only the ink receiving layer has sufficient properties. Additionally, a glossiness adjusting layer may be provided on a surface of an ink receiving layer. This glossiness adjusting layer preferably has the property that glossiness, by measuring the 60xc2x0 specular glossiness test according to the Japanese Industrial Standard Z8741, is 10 or more. As material of a glossiness adjusting layer, mixture materials of binder resin and pigment employed in an ink receiving layer may be employed as a coating solution. According to one method of providing the glossiness adjusting layer on the ink receiving layer in addition to the general coating method, for example, the coating solution is coated on base material which is inferior in adhesive property (for example, polyolefin resin film, ethylene tetrafluoride resin film, separatable silicone processed film, or the like); this coating surface is adhered to the surface of the ink receiving layer; after being dried, the base material is taken off; and the glossiness adjusting layer is formed. In order to maintain glossiness, it is preferable that the compounding ratio of the binding resin to the pigment in the glossiness adjusting layer be 5.0 to 50.0% by weight, and is more preferably 5.0 to 30.0% by weight. Weighting capacity, in which the glossiness adjusting layer exhibit excellent glossiness without impairing the function of the ink receiving layer, is preferably 3.0 to 25.0 g/m2, and is more preferably 5.0 to 15.0 g/m2.
The glossiness adjusting layer provided on the ink receiving layer according to the present invention preferably includes colloidal silica as a pigment component. The glossiness can be optionally adjusted by employing the colloidal silica which consists of different sized particles in an appropriate ratio. This glossiness adjusting layer can be adjusted by choosing the composition in an appropriate ratio so that the glossiness of the printed portion can be higher than that of the non printed portion, or can be conversely lower than it.